Malrotation of the Midgut

Malrotation of the Midgut

This disorder occurs in fetal development,
when the midgut supplied by
the superior mesenteric artery grows
too rapidly to be accommodated in
the abdominal cavity. Prolapse into
the umbilical cord occurs around the
sixth week of gestation. Between the
tenth and eleventh weeks, the midgut
retracts from its location at the exocelomic
umbilical stalk back into the
abdominal cavity. During this return,
the midgut undergoes a 270-degree
counterclockwise rotation about the
axis of the superior mesenteric artery,
followed by fixation to the posterior
abdominal wall. Malrotation
results from failure of the midgut to
properly rotate and affix itself to this
wall. This disorder occurs approximately
once in 500 live births.
The malrotated bowel itself does
not cause any significant problem.
However, the intestine remains free
on a narrow-based mesentery that
may twist around itself, producing a
midgut volvulus. In addition, dense
peritoneal bands (Ladd bands) (A)
may extend from the malpositioned
cecum across the second part of the
duodenum to the liver, posterior peritoneum,
or abdominal wall, thereby
causing abdominal obstruction. Lack
of fixation of the mesentery of the
colon and duodenum results in the
formation of potential hernial pouches.
Internal hernias--the most common
of which are right and left mesocolic
hernias--can cause entrapment
of the bowel.
Symptoms resulting from malrotation
may occur at any age. Half to
three quarters of patients who become
symptomatic do so in the first
month of life; approximately 90% of
patients are symptomatic within the
first year. Vomiting--often bilious--is
the usual presenting sign. Blood in
the stool suggests ischemia and possible
gangrene of the bowel. Abdominal
distension is usually not remarkable
in the initial stage. Once infarction
occurs, painful abdominal
distension and shock develop. Older
children with malrotation may present
with recurrent abdominal pain,
intermittent vomiting, chronic diarrhea,
malabsorption, and failure to
thrive.
Associated anomalies are found
in 30% to 60% of patients with malrotation.
These include diaphragmatic
hernia, omphalocele, gastroschisis,
intestinal atresia, imperforate anus,
Meckel diverticulum, mesenteric
cyst, Hirschsprung disease, congenital
heart disease, and heterotaxia.
Plain abdominal radiographs
may show a distended stomach and
proximal duodenum with a paucity of
air in the distal small bowel. Multiple
dilated loops of bowel or multiple airfluid
levels are usually not seen unless
the child has a volvulus complicated
by bowel infarction or an internal hernia
complicated by intestinal obstruction
(B). An upper GI tract series is
the study of choice and may help reveal
the abnormal position of the duodenojejunal
junction and duodenal
obstruction. This abnormality has a
characteristic "corkscrew," "coiled," or
"bird's beak" appearance (C).
Early surgical intervention is imperative
in a symptomatic patient to
minimize the risk of midgut gangrene.
Preoperative measures include
intravenous hydration to restore fluid
and electrolyte balance, nasogastric
suction, and intravenous antibiotics
(because a bowel resection may be
necessary). The procedure of
choice--the Ladd procedure--includes
evisceration of the midgut and
inspection of the mesenteric root,
counterclockwise derotation of the
volvulus, division of Ladd bands from
the cecum across the duodenum, appendectomy,
and placement of the
cecum in the left lower quadrant. The
appendectomy is performed because
the cecum is located in an atypical position,
which makes a future diagnosis
of appendicitis difficult. Nonviable
intestinal segments are resected and
primary anastomosis is performed. If
viability of the bowel remains in question,
the abdomen is closed and the
patient is given supportive therapy. A
second-look procedure is performed
at 24 to 36 hours.
For the asymptomatic child
younger than 2 years, timely repair is
indicated because most of the potential
complications occur at earlier
ages. The management of the older
asymptomatic patient is controversial.
Some experts believe that corrective
surgery should be performed
unless compelling contraindications
are present.

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